Magnetic Resonance Imaging (MRI) Practice Test

As the TR is increased, which of the following statements is true?

1. SNR increases

2. Available number of slices decreases

3. T2 information is minimized

4. 1 and 2 only

The correct answer is: 1 and 2 only

Increasing the repetition time (TR) in MRI has specific effects on the signal-to-noise ratio (SNR) and the number of slices that can be acquired. When the TR is increased, the amount of time that each slice remains relaxed before another excitation pulse occurs also increases. This additional time allows for greater signal recovery from tissues, which leads to an increase in SNR. It is critical in maximizing the amount of longitudinal magnetization available for the next pulse, resulting in clearer and more distinct images. Furthermore, extending TR impacts the total scan time, which can lead to a limitation on how many slices can be scanned within a certain timeframe, assuming a consistent acquisition volume and matrix size. Consequently, you may experience a decrease in the number of available slices that can be obtained within a specific total time limit for imaging. While it is true that increasing TR minimizes the contribution of T2 relaxation phenomena in terms of image quality and contrast, this aspect is less directly influenced by TR than the effects on SNR and slice availability. Therefore, the most precise and relevant statements are that SNR increases and the available number of slices decreases, making the combined selection the overall correct choice.